1. Field of the Invention
The present invention relates to a display device and an electronic appliance and, more specifically, to a display device and an electronic appliance capable of switching a range of viewing angles.
2. Description of the Related Art
Liquid crystal display devices (LCDs) as non-self luminous display devices have been widely used as display devices of various kinds of electronic appliances such as personal computers (PCs), portable telephone, television receiver sets, digital cameras, etc. When used for a television set in particular, it is sometimes desired to be capable of being viewed in a wide range of angles by decreasing changes in brightness and tones (to be of wide viewing angle). Because of such demands, liquid crystal display devices with a wide viewing angle that is achieved by employing IPS mode or VA mode have recently been put into practical use.
In the meantime, when using the liquid crystal display device for a personal computer or a portable telephone, for example, there is a case where a user wants to share a same display screen with others or a case where the user does not desire for others to look at the screen, depending on the time and circumstances. In that case, there may be required for the same liquid crystal display device to be able to switch the extent of viewing angles (viewing angle ranges) according to the conditions.
Techniques for switching the range of viewing angles of the liquid crystal display device are disclosed in following Patent Documents. Among those, Japanese Unexamined Patent Publication 10-319384 (Patent Document 1) discloses a technique which switches the extent of the viewing angles through adjusting the state of light that makes incident on a liquid crystal panel by utilizing a scattering-type liquid crystal layer that is capable of selecting a scattering state and a transparent state.
More specifically, first, FIG. 9 is a conceptual diagram for describing details of a structure of a conventional liquid crystal display device 500 disclosed in Patent Document 1. In the liquid crystal display device 500, emission light emitted from a surface light source (configured with a lamp tube 503, a light guide plate 504, and a light reflection film 505), which is collimated by a light-shielding unit 506 and becomes highly directive, makes incident on a scattering-type liquid crystal layer 502. The scattering-type liquid crystal layer 502 functions by application of a voltage, and either a scattering state or a transparent state is selected and set.
When the scattering-type liquid crystal layer is set to the scattering state, the highly directive incident light looses the directivity, and turns to diffused light and makes incident on a liquid crystal panel 501. Therefore, transmission display images of the liquid crystal display panel can be observed in a wide viewing angle range. In the meantime, when the scattering-type liquid crystal layer is selected to be in the transparent state, the light from the surface light source makes incident on the liquid crystal display panel 501 by keeping the high directivity. Therefore, transmitted display images on the liquid crystal display panel 501 can be viewed only within a narrow range of viewing angles. By utilizing this, the viewing angle of the liquid crystal display panel 501 can be switched through changing the voltage to be applied to the scattering-type liquid crystal layer 502.
Japanese Unexamined Patent Publication 2007-171674 (Patent Document 2) discloses a transflective liquid crystal display device capable of switching the viewing angles, as a structure in which a reflection part and a transmission part are provided alternately for each pixel of a liquid crystal element. Further, Japanese Unexamined Patent Publication 2006-140126 (Patent Documents 3) and Japanese Unexamined Patent Publication 2007-033813 (Patent Documents 4) disclose techniques which switch the extent of viewing angles by using a transparent/scattering switching element as an element that corresponds to the scattering-type liquid crystal layer 502 shown in FIG. 9.
However, there are following issues with the structure that switches the extent of the viewing angles in the liquid crystal display device 500 according to Patent Document 1 described above. In order to expand the adjustable range of the viewing angles in a narrow range in particular with this structure, it is necessary for the emission light collimated by the light-shielding unit 506 to have still higher directivity.
Therefore, it is necessary to set the height (thickness) of the light-shielding unit 506 to be more than a certain height. This is because sufficiently collimated highly directive emission light cannot be obtained, if the height of the light-shielding unit 506 is insufficient. Since it is necessary to secure the height (thickness) of the light-shielding unit 506 to some extent, there is a limit in thinning the thickness of the liquid crystal display device 500. Further, the height (thickness) of the light-shielding unit 506 has been always a problem not only for keeping the device to be thin but also for keeping the weight.
The liquid crystal display device of Patent Document 2 has the structure in which the reflection part and the transmission part are provided alternately within the liquid crystal element. With this structure, it is necessary to supply different video signals to each of the reflection part and the transmission part, in addition to the fact that the liquid crystal panel itself is in a special structure. Thus, it is necessary to have a plurality of driving circuits by corresponding to each of the parts. Therefore, the liquid crystal display device of Patent Document 2 always faces an issue of high cost.
Further, Patent Documents 3 and 4 are related to a constituent (louver) that corresponds to the light-shielding unit 506 in FIG. 9, and both require collimated emission light with still higher directivity. Therefore, the issue regarding reduction in the thickness of the liquid crystal display device 500 described above still remains. This issue regarding reduction in the thickness cannot overcome even if the techniques of Patent Documents 1-4 are combined.